Homemade CFRP mid engine sports car

Randy V

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I’d just screw in a long plastic mud-flap and remove it after inspection.... But I admittedly have a hard time following inanely stupid rules...
 
+1 with Randy
Was reading attentivly all your thread ; may I post some thoughts ?
On the 80's we had on aTrack french championship a Car builder building and selling some sport car with "almost "same Aerodinamics ; unfortunatly
they suffer lot of issues with cooling
Just scroll down this link and read what the ingineer ( was my friend competitor at the time !!) was talking about ;
Look at the test they did !!! ( remind the actual Ford VS Ferrari film !!!)
From what I remind some of the teams covered both sides in period ( racing purpose evidently ) but "collector owners" are today more inclined to come back to originals lines ;)
On another hand I have ( like some members stated before) to admit and recognise you are really talented with lines and drawings and your project need to be attentivly followed !! Congratulations ......

Some advise on CFRP ;
Being involved for quite long period in this process ( In charge of many LMP tubs and bodies fabrication )
Be aware that low temp CF is usable mostly for bodywork pur pose and not tubs due to the lack of hightstrenghs prepeg "twills" avaible ( hence this is valuable for very hight powered projects !!!
Infusion can be avery smart solution ( again mostly for the bodywork ) but building your CF tub will need to ingineer a honeycomb core use, so infusion could be a very very thought process VS prepeg ; you could not use one shot process and have to face the issue of bonding the honeycomb
in beetwen the 2 skins ( without talking about how to firmly insert aluminum stuff to get suspension picking points)
However as French people are saying ; "Paris ne s'est pas fait en un jour" !!! so I wish you plenty of determination and am sure you will be able few by few to discover how to solve those CFRP questions with "homebuilt" fashion !!!
There are some non expensive solutions that have been used by the past ......
Will follow your built with lot of interest
 
Thanks Michel, i'd planned to use PU foam instead of honeycomb, as its a lot easier for infusion .. and also a heck of a lot cheaper ! I don't intend to use it all over, just in local places where there are a lot of bending loads. Pretty much the whole body and structure will be made from heavy weight carbon twill, something like 600gsm or higher.

February update .. Finished prep of the buck and have now started to make the glass fibre molds .. at last .. i'm very happy to no longer be sanding !

I used a lot of coats of high build primer to get things flat and smooth, then moved on to a clear coat layer that could be polished to a gloss. Not sure if i really needed to do that or not, it added a lot of extra time, next time I might just sand primer to fine grit then polish the gelcoat on the mold. I read somewhere about putting a coloured pigment in each layer so you can see when you are breaking through, this was really great advice. Something else I learnt .. don't fibreglass in short sleeves (I had the heater on max to keep resin curing at right temp so I was very hot) .. not much fun trying to get it out of your arm hairs !

Aiming to finish all four parts of the rear body mold by end of Feb, then i'll move onto the front end. Gonna hack it apart a bit before paint & sand as i've changed my mind on the design.

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I used a lot of coats of high build primer to get things flat and smooth, then moved on to a clear coat layer that could be polished to a gloss. Not sure if i really needed to do that or not, it added a lot of extra time, next time I might just sand primer to fine grit then polish the gelcoat on the mold.
Very interesting! A lot of work but I would just say it's 100% easier polishing the buck before you take the mold than taking the mould and then polishing that. I know as have done it on my build, rubbed a part down with 400, waxed and then took the mould. I only did it once!!
 
Thanks Chris, yes i think you're right on that

just finishing off the 3rd part of the 4-part mould for the rear body. 1 more to go, then the moment of truth .. find out if the darn thing releases from the plug ! think i'm about a week away.
 
Last weekend was D-Day .. demoulding Day

Mixed success .. managed to get all 4 parts of the mould off .. but in many areas the plaster of the buck broke before the mould release. The bits of plaster left on the mould seem to come off alright with hammer and plastic chisel so i think i'm ok .. just a bit more work needed.

I've decided to finish off the rear end and mould the part. i.e. get the end before I make any more moulds for the rest of the car. But first, i'll practice the infusion process a few times on some flat sheets.

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been practising resin infusion before moving on the rear clam mould. Made a couple of flat panels that i'm gonna need later for the main body. This one is nearly 2mx1m and is eventually going to become the main rear bulkhead behind the seats.

things i have learned; (1) getting a full seal on the vacuum bag is a frustrating task. (2) the resin I am using works fine at 20 degrees but 15 and below it will take days to cure. I ended up bringing the part indoors to cure once infused and clamped off, I won't be able to do this on the big moulds .. so this is going to limit which months of the year I can be doing this.

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Its been an exciting weekend, I took advantage of the warm UK weather and moulded the rear bodywork !

Bit of a mixed success. The thing I was really worried about was achieving a full vacuum seal on the 4-piece split mould, but in the end this was not too hard and went OK. I was also really worried about releasing the part from the mould but again this was easy. The things that did not really go to plan were getting good consolidation in the corners, the fabric did not pull tight into the corners and there is are huge areas of bridging where the resin is really thick, this also led to lots of dry spots in other areas. I had always planned the paint the car so its nothing that I can't sort out with a bit of resin, filler and sanding. I plan to trim and finish the edges this weekend so I can offer it up to the buck and see how dimensionally good it is, then .. front body time :)


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I've been using my extra time at home recently to make a bit more progress on the project, the front end is now done and moulded too :)

demoulding the moulds from the buck was much easier this time, just popped off nice and easy, maybe the warmer weather. Had huge issues though with getting the split moulds to be vacuum tight, ended up with some bad areas. Not the end of the world for this part as I plan to paint it anyway, so can be corrected with filler, but I need to get the process sorted before I do the tub.

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started to work on something different for a bit, take a break from the big panel parts for a few weeks .. experimenting with the wishbones.

My plan is to wet lay CF over a 3D printed PLA core, the core being mainly to help me keep the right shape. I have embedded ali tubes for the bushes and ali blocks to tap for fixings after.

I finished one of the front lowers, the process seems to work ok .. a bit messy but easy to do. Need to do in many stages sanding smooth in between. My Son convinced me to use a hybrid CF/blue polyester fabric on top. I'm not convinced yet but I can live with it.

Next up is the front upper, the complicated pyramid shaped one. This will be rather harder and presumably rather messier. Wish me luck.

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CF wishbone factory running nicely. Put a TV in the garage for some entertainment while laminating. Finished full front LH side now, going to do the front RH too then get back onto outer body for the winter. Need to get the buck sitting tight on the windscreen then smooth and separate off the door sections.

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I have been slowly collecting certain parts as i finish areas of the design, buying things that i'm going to need to design other things around .. mostly boring things like seals and bushes .. but these were more exciting !

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Randy V

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CF wishbone factory running nicely. Put a TV in the garage for some entertainment while laminating. Finished full front LH side now, going to do the front RH too then get back onto outer body for the winter. Need to get the buck sitting tight on the windscreen then smooth and separate off the door sections.

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Amazing progress... Some first rate fabrication going on in your shop!
 
CF wishbone factory running nicely. Put a TV in the garage for some entertainment while laminating. Finished full front LH side now, going to do the front RH too then get back onto outer body for the winter. Need to get the buck sitting tight on the windscreen then smooth and separate off the door sections.

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Looks like a very nice quality finish Paul, and you show amazing progress and fabrication skills.

Some thoughts on the wishbones: I have quite a bit of experience in design and manufactor of CF wishbones, used to do those on an italian F1 car (no not that one, the other one).
What I know from those is that they needed an extreme amount of UD fibers (uni directional) to obtain the bending stiffness that they woudn't buckle or kink under the load. Granted, those arms were much longer and thinner than yours, but i'm not sure if you put deliberate thought into the direction of the fibers when laminating? CFRP is not a homogeneous material and charactaristics are vastly different depending on our layup design.
 
Hi Jasper, yep I used mostly UD, with a bit at 45 and 90. I found that with the wet layup over a tight shape its hard to keep it from wrinkling up under vacuum so I laminated it in 4-5 stages sanding back smooth inbetween. I ended up putting down extra 45deg layers as last layers each time as sacrificial sanding plies, so when sanding back you can tell from the fibre direction whether i've sanded too far and cut into any of the UD plies underneath. As these parts are somewhat safety critical I put down quite a lot more thickness than i'd calculated i would need for the loads, given they are hand made under less than ideal conditions - my garage is hardly a composites clean room

I do have a worry about in service temperature, the resin has a Tg of around 80deg, i'm not sure what kind of temperature to expect on these parts. I can put some reflective tape on the outer ends to protect from radiated head from the brakes but thats about it.
 
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